Dipole impedance matching device



Oct. 30, 1956 A. L. MUNZlG DIPOLE IMPEDANCE MATCHING DEVICE Z5 Sheets-Sheet l Filed March 22. 1952 Oct. 30, 1956 Filed Ngrch 22. 1952 A. L. MUNZIG DANCEMATCHING DEVICE 3 Sheets-Sheet 2 Oct. 30, 1956 ALL. MUNZIG" 2,769,169 DIPOLE IMPEDANCE. MATCHING DEVICE Filed March 22. 1952 i 5 Shets-Sheet 3 United States PatentO DIPOLE IMPEDANCE MATCHING DEVICE Application March 22, 1952, serial No. 277,924

8 Claims." (Cl. 343-822) .fMy invention relates to dipole antennas, and more particularly to a meansfor coupling a dipole antenna to a transmission line to provide an automatic impedance match therebetween.

, A common way of matching a center-fed, half-wave dipole to a transmission line, is to shorten the antenna so that a capacitative impedance is presented at its input. Then a tuning stub is connected to the dipole input in parallel with the transmisison line. This stub presents an inductive reactance to the input, and this inductive reactance can be varied with relation to the capacitative impedance of the dipole at its input so that an eflective pure resistance is produced to match the line impedance. Such a match however, is not automatic and'requires considerable experimentation and stub cutting to properly tune the stub.

. It is an object of the present invention to provide a means automatically matching a half-wave center-fed dipoleto a transmission line.

flt is another object of the invention to providea simple automatic impedance match between a center-fed half-wave dipole and a transmission line.

In brief, the present invention in one useful form utilizes a half-wave center-fed dipole, having parallel quarter-wave antenna input conductorsconnected, one to each quarter-wave dipole element, preferably at right angles thereto. A 300 ohm transmission line is terminated in two quarter-wave line conductors. One quarter-wave line conductor is paralleled to and closely capacitatively coupled to one of the quarter-wave antenna input conductors; The other quarter-wave line conductor is similarly closely coupled to the other antenna input conductor. The result is an automatic impedance match between the transmission line and the dipole antenna. In other forms, :the coupling can be to quarter wave sections of the transmission line, provided the match is made at any line length 'where there is a multiple of a quarter-wave length be- :tween the quarter-wave coupling conductors and the antenna. input. Thus, a number of transmission lines, all

properly matched to the antenna can be taken oflother lines.

My invention will be more fully understood by reference to the drawings in which:

Figure 1 is a perspective'view of a center-fed halfwave dipole matched to a transmission line in accordance with the present invention. 7

Figure 2 is a? cross sectional view taken as indicated by the line 22 in Figure 1. V

I Figure 3 is a circuit diagram equivalent to the electrical characteristics of the system of Figure 1. I

1 Figure 4 isa circuit diagram of an impedance mate of a lin eto stacked dipoles. 1

Figure 5 is acircuit diagram ofan impedance match of a line to a double V type of dipole antenna.

Figure 6 is a circuit diagram showing a main transmission line matched to a dipole, with matched side lines, so that a single antenna can serve a plurality of receivers.

Referring first to the embodiment of the invention 2,769,169 Patented Oct. 30, 1956 shown in Figures 1 and 2, a mast 1 supports a splitinsulator 2 through bracket 3; insulator 2 being used to support a center-fed half-wave dipole antenna 4. Antenna 4 comprises a pair of quarter-wave dipole elements 5 preferably coextensive and formed from metal rod or tubing as customarily used for such dipoles. The dipole elements 5, for convenience, may at their closest approach point he turned downwardly with right angle bends 6 to form two parallel quarter-wave antenna input conductors 7.

A quarter-wave line conductor 8 is closely coupled to each of the antenna input conductors 7, being insulated from each other as by the use of insulating sleeves 9. The spacing of the coupled conductors has been exaggerated in Figure 1 for clarity of illustration.

Both insulating sleeves 9, and their conductors 7 and '8 p are then clamped in split insulator 2 to support'the'antenna 4 and the coupling system.

An insulated twin-wire transmission line 10, such as a 300 ohm line, for example, has the wires 11 thereof con nected, one to each line conductor 8. The transmission line 10 is then extended to a radio or radar receiver (or transmitter) input (or output).

Since a one quarter-Wave length line acts similarly to a transformer, in that the impedance at one end appears ditferently at the other, the system described is electri-' cally equivalent to closely coupling two tuned circuits wherein the impedances of both are matched to each other, providing an electrical characteristic equivalent as shown in Figure 3, with a resultant automatic impedance match. i

Measurements have shown a great improvement in standing wave ratio of about lto 7 when using the automatic match of the present invention, with respect to the same dipole antenna connected directly to the transmission line. No stub cutting or tuning is required, and the antenna does not need to be shortened.

It is preferred that the spacing of the line conductors 8 along their coupled extent, be substantially the same as the wires in the twin line 10. Thus the match will be automatic to lines of different spacing and ohmage.

If the quarter wave coupled matching section is cut for the lowest frequency to be used, it will operateefli ciently on its even and odd harmonics. Thu's broad frequency response characteristics are inherent.

It has further been found that even though the antenna impedance is somewhat changed, due to the addition of reflectors or directors, or by folding or lengthening (harmonic operation), an impedance match will still result due to the very close couplingin the matching section.

The automatic impedance match above described'is of course useful for both receiving and transmitting antennas and in the latter case the power handled and transferred in the matching section is limited only by the insulation factor between the closely coupled conductors.

, In Figure 4 the transmission line 10 is shown as being connected at one end to a television receiver 20 and matched at the other end to stack halfwave dipoles 4a and 4b, one of these dipoles 4a being disposed one half wave above the other dipole 4b. Line 10 is continued through an intermediate quarter-wave matching section 21 for dipole 4b similar to that described in conjunction with the dipole 4 in Figure 1, and after a line wire cross over 22 enters a terminal quarter-wave matching section 23 for dipole j4a exactly, the same as thatdescribed;

in both forward and rear Vs. results.

As an automatic impedance match can be made to the transmission line at any quarter-wave length thereof being a multiple of a quarter-wave, the match of the present invention is ideally suited for the connection of a number of receivers to a single antenna of the dipole type, as shown, for example in Figure 6.

Here, the dipole 4 is connected through a dipole matching section 30 to line 10 which runs directly to a television receiver for example. Quarter-wave matching section a, 30b, and 30c connected respectively to side lines 10a, 10b, and 100, are positioned along line 10 wherever the conditions of n quarter-wave lengths obtain, measured from the antenna 4. If desired sub-side lines X may be matched off any of the side lines such as 10a and 10c, using quarter-wave matching sections 30X and maintaining the quarter-wave spacing. Thus a large number of receivers 20 can be supplied from a single antenna, for use in apartment houses for example. To provide greater antenna gain stacked dipoles of any type desired may be used if desired, matched to the main transmission line 10 as taught herein with respect to Figure 4.

It will thus be seen that by using quarter-wave closely coupled matching sections spaced at n quarter-wave distances from the antenna, both main and auxiliary transmission lines can readily be automatically matched to a dipole antenna.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise several preferred forms of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

1. Means for matching a center fed dipole antenna to a twin wire transmission line for operation over a desired frequency band, which comprises a rigid integral extension of each dipole element, said extensions aligned parallel to each other and at right angles to said dipole elements at their closest approach point, aid extensions being electrically open from each other, a rigid coupling conductor closely and capacitively coupled to each of said extensions along the length thereof, said coupling conductors being electrically open from each other, a single insulated clamping means around the coupling members for supporting said extensions and said coupling conductors in the claimed position with said coupling conductors spaced apart the same distance as the two line wires of said transmission line, one line wire of said transmission line connected to the end of one of said coupling conductors, and the other transmission line wire connected to a similar end of the other coupling conductor, said dipole extensions and said coupling conductors all being a quarter-wavelength long at the lowest frequency of said band.

2. Apparatus in accordance with claim 1 wherein said coupling conductors are coupled to said extension by means of a continuous insulating sleeve running the length of the quarter-wave coupling section.

3. Means for matching a center fed antenna to a twin wire transmission line, comprising an assembly of four parallel conductors each a quarter-wavelength long at the lowest frequency to be encountered, said conductors being electrically open from each other, the first two of An automatic match said conductors adapted to be connected at one end thereof to adjacent respective feed points of said antenna substantially at right angles to the elements of said antenna, the second two conductors each closely and capacitively coupled to respective ones of said first two conductors along the length thereof by means of a continuous insulating sleeve, said second two conductors being spaced apart substantially the same distance as the twin wires of said transmission line and being adapted to be respectively connected at one end thereof to said twin wires, and insulating means for supporting said assembly on a mast of said antenna, the remaining ends of said four conductors being open.

4. An antenna system comprising in combination, a first pair of quarterwave parallel wire stubs closely and capacitatively coupled, a second pair of quarter-wave parallel wire stubs closely and capacitatively coupled, said stub pairs being positioned in spaced parallel relation, a first dipole element directly connected to an end of one of said first pair of stubs, a second dipole element directly connected to an end of one of said second pair of stubs with said dipole connections adjacent, a spaced parallel conductor transmission line connected across the ends of the stubs in said pairs not connected to said dipole elements at the opposite ends of said pairs from said dipole connections, the remaining ends of said stubs, being open, the spacing of said pairs being substantially the same as the spacing of the conductors of said transmission line.

5. System in accordance with claim 4 wherein said transmission line is a 300 ohm line.

6. System in accordance with claim 4 wherein each of said stub pairs are molded into integral insulation.

7. Means for impedance matching a center fed dipole antenna to a twin spaced wire transmission line for operation over a desired frequency band which comprises a first pair of quarterwave parallel wire stubs closely and capacitatively coupled, a second pair of quarterwave parallel wire stubs closely and capacitatively coupled, means for holding said pairs in spaced parallel relation, means for directly connecting a dipole element to an end of one of said first pair of stubs, means for connecting a dipole element to an end of one of said second pair of stubs, with said dipole connections adjacent, means for connecting a twin wire transmission line across the ends of the stubs in said pair not having said dipole connections, said transmission line connections being at the opposite ends of said pairs from said dipole connections, the spacing of said pairs being substantially the same as the spacing of the Wires in the transmission line to be connected to said impedance matching means.

8. An antenna system comprising a pair of dipole elements, a twin lead parallel wire transmission line open at one end thereof, a quarterwave matching wire attached to each of said dipole elements at the adjacent ends thereof, one of said matching wires extending close to and parallel to one of the wires of said transmission line, the other of said matching wires extending close to and parallel to the other wire of said transmission line, said matching wires being open ended, the open end of said transmission line being disposed adjacent the connection of said matching wires to said dipole elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,159,648 Alford May 23, 1939 2,259,510 Alford Oct. 21, 1941 2,417,290 Brown Mar. 11, 1947 2,530,048 Driscoll Nov. 14, 1950 

